Bhagirathi and Alaknanda are two major headstreams that originate in western Himalayas of India and, upon their confluence at Devprayag, give rise to much revered River Ganga. Bhagirathi is spiritual source of Ganga but, interestingly, Alaknanda is seen to influence much of hydrological and ecological essence of region by draining larger area with comparatively more discharges and supporting a larger and diverse bio-reserve. Notwithstanding with these seemingly calming observations, developmental pressure in the form of more than 30 operational and under construction run-of-river hydropower projects has indeed fuelled an ever growing apprehension that the basin may have already reached a tipping stage.

Accordingly, this study attempts to develop an understanding of the state of natural equilibrium between hydrological and ecological response systems of Alaknanda. The study seeks to assess the current hydrologic regime for its compatibility with ecological demands assessed for endangered Golden Mahseer-Tor putitora, a keystone fish species holding highest trophic level in the aquatic food web of Alaknanda. For this, variations in Golden Mahseer habitat (Weighted Usable Area) with variations in seasonal flow have been analysed using PHABSIM-habitat modelling tool, for its three life stages. Non-availability of detailed and reliable data on observed bed morphology has long been a major hurdle in similar eco-hydraulic study initiatives, including the present study, in India. Accordingly, this study is an initiative that makes use of SRTM 1 Arc-Second Global digital elevation data in support with sparse observed cross sections and, in recognition of these difficulties, suggests 'most suitable’ range of e-flows.